1. Field of the Invention
The present invention relates to an electronic still camera such as an SLR electronic still camera incorporating a focal plane shutter and an image pick-up unit.
2. Description of the Related Art
In recent years, various types of electronic still cameras (e.g., SLR digital cameras) having camera bodies originally designed for conventional focal plane shutter cameras using silver-salt film (e.g., conventional SLR cameras) have been developed. FIG. 11 shows fundamental optical elements of a conventional SLR electronic still camera having a camera body (not shown) originally designed for a conventional SLR camera using silver-salt film. Light rays which are passed through a photographing lens L are reflected upward by a quick-return mirror 13 to pass through a focusing screen 15 which lies in a plane provided at a point optically equivalent to an image point (design image point) IP formed through the photographing lens L. Subsequently, the light rays which are passed through the focusing screen 15 are converged through a condenser lens 17, and are reflected by a pentagonal prism (image-erecting system) 19 to exit from an eyepiece 21. The user views the image focused on the focusing screen 15 as an erect image through the eyepiece 21, the pentagonal prism 19 and the condenser lens 17. Upon a shutter release operation, the quick-return mirror 13 comes up and a set of focal-plane shutter blades (shutter curtains) 23 of a focal plane shutter open so that an object image is formed on a plane (image plane including the image point IP) perpendicular to an optical axis 0. Accordingly, the object image which is identical to the object image focused on the focusing screen 15 and which has a focus state identical to that of the object image focused on the focusing screen 15 is formed on an image plane which passes the image point IP, and is captured by a CCD image sensor (image pick-up device) 101 positioned behind the set of focal-plane shutter blades 23.
The camera body of such a conventional SLR camera using silver-salt film is designed so that the image point IP is positioned on a film surface immediately behind the set of focal-plane shutter blades 23. Therefore, the spacing between the rear face of the set of focal-plane shutter blades 23 and the image point IP is very small.
The CCD image sensor 101 is provided with an imaging surface 103, and is further provided in front of the imaging surface 103 with various optical elements such as a cover glass, an optical low-pass filter and an infrared absorption filter. Due to this structure, the spacing between a frontmost surface 101a of the CCD image sensor 101 and the imaging surface 103 is large. Therefore, the CCD image sensor 101 interferes with the set of focal-plane shutter blades 23 if the CCD image sensor 101 is disposed so that the imaging surface 103 includes (coincides with) the image point IP, or the imaging surface 103 deviates from the image point IP if the CCD image sensor 101 is disposed not to interfere with the set of focal-plane shutter blades 23.